Ion milling system

ABSTRACT

To provide an ion milling system that can suppress an orbital shift of an observation electron beam emitted from an electron microscope column, the ion milling system includes: a Penning discharge type ion gun  100  that includes a permanent magnet  114  and that generates ions for processing a sample; and a scanning electron microscope for observing the sample, in which a magnetic shield  172  for reducing a leakage magnetic field from the permanent magnet  114  to the electron microscope column is provided.

TECHNICAL FIELD

The present invention relates to an ion milling system.

BACKGROUND ART

An ion milling system is a processing system that causes bombardment ofa sample by accelerated ions and that cuts the sample using sputteringthat the ions dislodge atoms and molecules. Furthermore, a mask thatserves as an ion beam masking shield is placed on an upper surface ofthe sample to be processed, and a protruding portion of the sample froma mask end surface (exposed portion thereof that is not covered with themask) is sputtered, whereby the sample can be processed to have a smoothcross-section. The ion milling system is employed for a target such asmetal, glass, ceramics, an electronic component, or a compositematerial. For example, if the electronic component is a target, the ionmilling system is used to create a cross-section sample for acquisitionof a morphological image, a sample composition image, and a channelingimage by a scanning electron microscope or for acquisition by X-rayanalysis, crystal orientation analysis, or the like for use applicationsincluding evaluation of an internal structure, a cross-sectional areashape, and a film thickness and analysis of a crystalline state, afailure, and a foreign substance cross-section.

Demand is high for combination of the ion milling system with anelectron microscope system for the purpose of improving usability,responding to demand of three-dimensional analysis, responding to demandof analysis of a material that cannot be exposed to the atmosphere, orthe like. Patent Document 1 discloses an ion milling system in which anelectron microscope is mounted as a technique for checking a progress ofmilling processing while a sample is being subjected to the millingprocessing by an ion beam. Patent Document 2 discloses a method ofobserving an internal structure of a sample by a scanning electronmicroscope while the sample is gradually subjected to ion millingprocessing starting with a surface of the sample, as a method ofthree-dimensionally analyzing the internal structure of the sample.Patent Document 3 discloses a method with using a scanning electronmicroscope provided with a sample preprocessing system in which aniongun is mounted, the method sequentially observing a structure of asample in a depth direction from a surface of the sample by a scanningelectron microscope while the sample is gradually subjected to ionpolishing starting with the surface of the sample in the same vacuum asthat in which the structure is observed.

PRIOR ART DOCUMENT Patent Document

Patent Document 1: International Publication No. WO2012/060416

Patent Document 2: JP-2000-195460-A

Patent Document 3: JP-H08-298092-A

SUMMARY OF THE INVENTION Problem to be Solved by the Invention

Mounting a scanning electron microscope (SEM) in an ion milling systemis expected to bring the following advantages. Even if an observationtarget to be processed by the ion milling system is a foreign substancecross-section having a dimension, for example, equal to or smaller than1 μm, alignment of a sample processing position can be easily performed.In addition, the cross-section during or after processing by the ionmilling system can be observed by the SEM within the same system as thatin which the processing is performed. The inventors, therefore,conducted a study about an ion milling system in which an SEM wasmounted. A result of the study will be explained below.

The inventors conducted a study about an ion milling system thatemploys, as an ion gun, a Penning discharge type ion gun having a simpleconfiguration and being small in size. The Penning discharge type iongun is configured such that electrons emitted from cathodes make aturning motion by a magnetic field from a permanent magnet and strikeagainst gas introduced into the ion gun, thereby causing ionization. Theelectrons make a reciprocating motion between electrodes at the samepotential by disposing the cathodes on both ends of an anode; thus, itis possible to make an orbit of the electrons long and to improveionization efficiency. Part of cations generated in an ionizationchamber are passed through a cathode outlet hole, accelerated by anaccelerating electrode, and emitted to outside from an acceleratingelectrode outlet hole. Improving a milling performance requires anincrease in an amount of ions emitted from the ion gun. To address thechallenge, high plasma density is essential, and it is necessary toensure a long electron orbit by forming a magnetic field at a highmagnetic flux density. Since the Penning discharge type ion gun isconfigured such that the permanent magnet is provided thereinside, aleakage magnetic field from the ion gun has an adverse influence on anelectron beam during electron microscope observation. It was discoveredthat since an electron emitted from an electron microscope column takeson a property that an orbit thereof is curved even by a very weakmagnetic field, the ion milling system had a problem that the electronbeam from an electron microscope was largely curved.

The present invention has been achieved in light of these respects, andan object of the present invention is to provide an ion milling systemthat can suppress an orbital shift of an electron beam emitted from anelectron microscope column.

Means for Solving the Problem

To attain the object, according to one embodiment, there is provided anion milling system including: an ion gun that includes a permanentmagnet and that generates ions for processing a sample; and a scanningelectron microscope that observes the sample, in which the ion millingsystem includes a magnetic shield that reduces a leakage magnetic fieldfrom the permanent magnet.

Effect of the Invention

According to the present invention, it is possible to provide an ionmilling system that can suppress an orbital shift of an electron beamemitted from an electron microscope column.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an overall cross-sectional configuration diagram showing anexample of an ion milling system (according to each embodiment of thepresent invention or in a case in which the ion milling system includesan ion gun without a magnetic shield).

FIG. 2 is a cross-sectional configuration diagram for explaining the iongun that does not include a magnetic shield structure.

FIG. 3 is a cross-sectional configuration diagram showing an example(configurations 1 and 2) of an ion gun (including the magnetic shieldstructure) in the ion milling system according to a first embodiment ofthe present invention.

FIG. 4 is a cross-sectional configuration diagram showing anotherexample (configuration 3) of the ion gun (including the magnetic shieldstructure) in the ion milling system according to the first embodimentof the present invention.

FIG. 5 is a cross-sectional configuration diagram showing anotherexample (configuration 4) of the ion gun (including the magnetic shieldstructure) in the ion milling system according to the first embodimentof the present invention.

FIG. 6 is a cross-sectional configuration diagram showing anotherexample (configuration 5) of the ion gun (including the magnetic shieldstructure) in the ion milling system according to the first embodimentof the present invention.

FIG. 7 is a cross-sectional configuration diagram showing anotherexample (configuration 6) of the ion gun (including the magnetic shieldstructure) in the ion milling system according to the first embodimentof the present invention.

FIG. 8 is a cross-sectional configuration diagram showing anotherexample (configuration 7) of the ion gun (including the magnetic shieldstructure) in the ion milling system according to the first embodimentof the present invention.

FIG. 9 is a cross-sectional configuration diagram showing anotherexample (configuration 8) of the ion gun (including the magnetic shieldstructure) in the ion milling system according to the first embodimentof the present invention.

FIG. 10 shows an intensity of a magnetic field leaking from the ion gun,in which (a) shows intensities in cases of the configurations 3, 4, 5,and 8 and a case of the ion gun without the magnetic shield, and (b)shows intensities in cases of the configurations 1, 2, 6, and 7 and thecase of the ion gun without the magnetic shield.

FIG. 11 shows an axial magnetic field intensity within the ion gun, inwhich (a) shows intensities in the cases of the configurations 3, 4, 5,and 8 and the case of the ion gun without the magnetic shield, and (b)shows intensities in the cases of the configurations 1, 2, 6, and 7 andthe case of the ion gun without the magnetic shield.

FIG. 12 shows axial magnetic field intensities within the ion gunwithout the magnetic shield (with mounted magnets having differentcharacteristics used as parameters).

FIG. 13 shows axial magnetic field intensities within the ion gun thathas the configuration 2 shown in FIG. 1 (with the mounted magnets havingthe different characteristics used as parameters).

FIG. 14 shows an example of a beam profile for explaining effects of thepresent embodiment.

FIG. 15 is a cross-sectional configuration diagram showing an example ofan ion gun (including an accelerating electrode guide member) in the ionmilling system according to a second embodiment of the presentinvention.

FIG. 16 is a cross-sectional configuration diagram showing anotherexample of the ion gun (including the accelerating electrode guidemember) in the ion milling system according to the second embodiment ofthe present invention.

MODES FOR CARRYING OUT THE INVENTION

After conducting a study about the problems, the inventors have decidedto add a magnetic shield to a Penning discharge type ion gun. It isthereby possible to reduce a leakage magnetic field from a permanentmagnet installed within the ion gun.

Specifically, the ion gun includes, for example, a gas supply mechanismthat supplies gas into the ion gun; an anode which is disposed withinthe ion gun and to which a positive voltage is applied; two cathodesthat generate a potential difference between the anode and the cathodes;a cathode ring and an insulator; and a permanent magnet, causeselectrons emitted from the two cathodes to turn by the magnetic field,ionizes the gas by the turning electrons, and emits generated ions tooutside of the ion gun by an accelerating electrode, in which theaccelerating electrode is formed from a ferromagnetic material. Thisconfiguration thereby reduces the leakage magnetic field from the iongun and sufficiently suppresses an orbital shift of an electron beamemitted from an electron microscope column.

In that case, the ferromagnetic material can be formed on a surface, onwhich the accelerating electrode is disposed, of an ion gun base.

Alternatively, an outer peripheral surface of the accelerating electrodeformed from stainless steel and the surface, on which the acceleratingelectrode is disposed, of the ion gun base can be covered with theferromagnetic material.

Alternatively, an inner peripheral surface of the accelerating electrodeformed from stainless steel and the surface, on which the acceleratingelectrode is disposed, of the ion gun base can be covered with theferromagnetic material.

Alternatively, a magnetic shield structure formed from a ferromagneticmaterial can be formed on an outer side of the ion gun, and theferromagnetic material can be formed on the surface, on which theaccelerating electrode is disposed, of the ion gun base.

Alternatively, the cathode ring can be formed from the ferromagneticmaterial.

In another alternative, the magnetic shield structure formed from theferromagnetic material can be formed on an inner side of theaccelerating electrode.

Preferably, the ferromagnetic material includes permalloy, pure iron,nickel, copper, molybdenum, and a material containing at least one typeof permalloy, pure iron, nickel, copper, and molybdenum as a maincomponent.

Adding the magnetic shield structure to the ion gun makes it possible tosufficiently reduce the leakage magnetic field from the permanent magnetdisposed within the ion gun.

Furthermore, changing a structure of a magnetic shield electrode addedto the ion gun makes it possible to control an axial magnetic fieldintensity within the ion gun. It is thereby possible to select anoptimum axial magnetic field intensity for deriving an ion gunperformance; thus, it is possible to obtain a far higher milling ratethan that according to a conventional technique.

Preferred embodiments of the present invention will be explainedhereinafter with reference to the drawings. It is noted that the samereference characters denote the same constituent elements.

First Embodiment

An ion milling system will be explained with reference to the drawings.FIG. 1 is an overall cross-sectional configuration diagram showing anexample of the ion milling system. Constituent elements necessary togenerate ions are disposed within a Penning discharge type ion gun 101,and an irradiation system for irradiating a sample 106 with an ion beam102 is formed. Constituent elements necessary to generate an electronbeam 162 are disposed within an electron microscope column 161, and anirradiation system for irradiating the sample 106 with the electron beam162 is formed. A gas source 142 is connected to the ion gun 101 via agas supply mechanism 141, and a gas flow rate controlled by the gassupply mechanism 141 is supplied into an ionization chamber of the iongun 101. Irradiation of the ion beam 102 and an ion beam current of theion beam 102 are controlled by an ion gun control section 103. The ionbeam current of the ion beam 102 is measured by current measurementmeans 151. A current probe 153 also functions as an ion beam shutter andhas a mechanism actuated by a current probe drive section 152. A vacuumchamber 104 is controlled to have an atmospheric pressure or to be in avacuum by an evacuation system 105. The sample 106 is held on a samplestage 107 and the sample stage 107 is held by a sample stage drivesection 108. The sample stage drive section 108 includes all ofmechanism elements that can be drawn out of the vacuum chamber 104 whenthe vacuum chamber 104 is open to the atmosphere, and that can tilt thesample 106 at an arbitrary angle with respect to an optical axis of theion beam 102. It is thereby possible to adjust the sample in desireddirections during processing by the ion beam and observation by theelectron beam. A sample stage drive control section 109 can control thesample stage drive section 108 in such a manner that the sample istilted and swings longitudinally or horizontally, and can control aspeed of the sample stage drive section 108.

FIG. 2 is a cross-sectional view showing configurations of the ion gun101 that does not include a magnetic shield structure and relevantperipheral parts. The ion gun 101 is configured with the gas supplymechanism 141 that supplies gas into the ion gun, an anode 113, a firstcathode 111 and a second cathode 112, a permanent magnet 114, anaccelerating electrode 115, an insulator 116, and a cathode ring 119,and is secured to an ion gun base 117. The ion gun control section 103is electrically connected to a discharge power source 121 and anaccelerating power source 122, and controls a discharge voltage and anaccelerating voltage. It is noted that reference character 118 denotesthe ionization chamber, reference character 131 denotes an anode outlethole, reference character 132 denotes a cathode outlet hole, andreference character 133 denotes an accelerating electrode outlet hole.

The first cathode 111 and the second cathode 112 are made of pure ironthat is a ferromagnetic substance, and form, along with the permanentmagnet 114 that is a magnetomotive force, a magnetic circuit. On theother hand, the accelerating electrode 115, the cathode ring 119, andthe ion gun base 117 are made of stainless steel (SUS: Steel Special UseStainless), and the accelerating electrode 115, the cathode ring 119,and the ion gun base 117 as well as the insulator 116 made of aluminaand the anode 113 made of aluminum are not, therefore, included in themagnetic circuit.

Since the Penning discharge type ion gun as described above isconfigured such that the permanent magnet is provided inside, a leakagemagnetic field from the ion gun has an influence on the electron beamduring electron microscope observation. Even a slight electron beamorbital shift causes a problem particularly when a specific microscopicregion is observed. Since an electron emitted from the electronmicroscope column takes on a property that an orbit thereof is curved bya very weak magnetic field, the electron beam is largely curved duringconversion of the accelerating voltage or the like and an observationimage that is being observed is largely shifted, accordingly in the ionmilling system in which the electron microscope is mounted. To avoidthis observation image shift, it is necessary to suppress the leakagemagnetic field from the ion gun.

FIG. 3 is a cross-sectional configuration diagram showing an example ofan ion gun (including a magnetic shield structure, hereinafter, referredto as “magnetic shield structure ion gun”) in the ion milling systemaccording to the present embodiment. The ion milling system according tothe present embodiment has a configuration such that the ion gun 101 inFIG. 1 is replaced by a magnetic shield structure ion gun 100. Thepresent Penning discharge type magnetic shield structure ion gun 100includes the gas supply mechanism 141 that supplies gas into the iongun, the anode 113 which is made of, for example, aluminum, which isdisposed within the ion gun, and to which a positive voltage is applied,the first cathode 111 and the second cathode 112 which are made of, forexample, pure iron and which generate a potential difference between theanode 113 and the first and second cathodes 111 and 112, the cathodering 119 made of, for example, stainless steel and the insulator 116made of, for example, alumina, and the permanent magnet 114 of, forexample, neodymium. The present Penning discharge type magnetic shieldstructure ion gun 100 is characterized in that employing a magneticshield 171 made of, for example, permalloy as the accelerating electrodemakes it possible to obtain a sufficient shielding effect, reduce theleakage magnetic field from the magnetic shield structure ion gun 100,and sufficiently suppress the orbital shift of the electron beam 162emitted from the electron microscope column 161 (configuration 1).

Alternatively, in the magnetic shield structure ion gun 100, forming themagnetic shield 171 made of, for example, pure iron in place of themagnetic shield made of permalloy as the accelerating electrode makes itpossible to obtain a magnetic shielding effect, reduce the leakagemagnetic field from the magnetic shield structure ion gun 100, andsufficiently suppress the orbital shift of the electron beam 162 emittedfrom the electron microscope column 161 (configuration 2).

FIG. 4 is a cross-sectional configuration diagram showing anotherexample of the magnetic shield structure ion gun in the ion millingsystem according to the present embodiment. The present Penningdischarge type magnetic shield structure ion gun 100 is characterized inthat forming the accelerating electrode from a magnetic shield 172 madeof, for example, pure iron, and additionally forming the magnetic shield172 made of, for example, pure iron on a surface, on a side of which theaccelerating electrode is disposed, of the ion gun base 117 made of, forexample, stainless steel make it possible to further reduce the leakagemagnetic field from the magnetic shield structure ion gun 100 andsufficiently suppress the orbital shift of the electron beam 162 emittedfrom the electron microscope column 161 (configuration 3).

FIG. 5 is a cross-sectional configuration diagram showing yet anotherexample of the magnetic shield structure ion gun in the ion millingsystem according to the present embodiment. The present Penningdischarge type magnetic shield structure ion gun 100 is characterized inthat covering an outer peripheral surface of the accelerating electrode115 made of, for example, stainless steel and the surface, on aside ofwhich the accelerating electrode 115 is disposed, of the ion gun base117 made of, for example, stainless steel with a magnetic shield 173made of, for example, pure iron makes it possible to reduce the leakagemagnetic field from the magnetic shield structure ion gun 100 andsufficiently suppress the orbital shift of the electron beam 162 emittedfrom the electron microscope column 161 (configuration 4).

FIG. 6 is a cross-sectional configuration diagram showing still anotherexample of the magnetic shield structure ion gun in the ion millingsystem according to the present embodiment. The present Penningdischarge type magnetic shield structure ion gun 100 is characterized inthat covering an inner peripheral surface of the accelerating electrode115 made of, for example, stainless steel and the surface, on aside ofwhich the accelerating electrode 115 is disposed, of the ion gun base117 made of, for example, stainless steel with a magnetic shield 174made of, for example, pure iron makes it possible to reduce the leakagemagnetic field from the magnetic shield structure ion gun 100 andsufficiently suppress the orbital shift of the electron beam 162 emittedfrom the electron microscope column 161 (configuration 5).

FIG. 7 is a cross-sectional configuration diagram showing yet anotherexample of the magnetic shield structure ion gun in the ion millingsystem according to the present embodiment. The present Penningdischarge type magnetic shield structure ion gun 100 is characterized inthat forming a magnetic shield 175 made of, for example, a ferromagneticmaterial such as pure iron in an outermost portion of the ion gun andforming the magnetic shield 175 made of, for example, pure iron on thesurface, on a side of which the accelerating electrode 115 made of, forexample, stainless steel is disposed, of the ion gun base 117 made of,for example, stainless steel make it possible to reduce the leakagemagnetic field from the magnetic shield structure ion gun 100 andsufficiently suppress the orbital shift of the electron beam 162 emittedfrom the electron microscope column 161 (configuration 6).

FIG. 8 is a cross-sectional configuration diagram showing still anotherexample of the magnetic shield structure ion gun in the ion millingsystem according to the present embodiment. The present Penningdischarge type magnetic shield structure ion gun 100 is characterized inthat forming the cathode ring from a magnetic shield 176 made of, forexample, pure iron makes it possible to reduce the leakage magneticfield from the magnetic shield structure ion gun 100 and sufficientlysuppress the orbital shift of the electron beam 162 emitted from theelectron microscope column 161 (configuration 7).

FIG. 9 is a cross-sectional configuration diagram showing yet anotherexample of the magnetic shield structure ion gun in the ion millingsystem according to the present embodiment. The present Penningdischarge type magnetic shield structure ion gun 100 is characterized inthat forming a magnetic shield 177 made of, for example, pure iron on aninner side of the accelerating electrode 115 made of, for example,stainless steel makes it possible to reduce the leakage magnetic fieldfrom the magnetic shield structure ion gun 100 and sufficiently suppressthe orbital shift of the electron beam 162 emitted from the electronmicroscope column 161 (configuration 8).

FIG. 10 shows an intensity of the magnetic field leaking from themagnetic shield structure ion gun 100 having each of the configurationsin the ion milling system according to the present embodiment, in which(a) shows intensities in cases of the configurations 3, 4, 5, and 8 anda case of the ion gun without the magnetic shield, and (b) showsintensities in cases of the configurations 1, 2, 6, and 7 and the caseof the ion gun without the magnetic shield. The intensities are obtainedas a result of calculating leakage magnetic flux densities by a magneticfield simulator in a case of employing a neodymium magnet having acoercive force of 859 kA/m at a residual magnetic flux density in arange from 1250 to 1320 mT as the permanent magnet 114 mounted in theion gun. In FIG. 10, a horizontal axis indicates a distance from a tipend of the ion gun and a horizontal axis indicates an intensity of theleakage magnetic field from the ion gun. For example, in a region 80 mmapart from the tip end of the ion gun, a leakage magnetic fieldintensity is 0.69 mT for the ion gun 101 to which the magnetic shield isnot added. On the other hand, the leakage magnetic field intensity canbe reduced to 0.12 mT for the magnetic shield structure ion gun with theconfiguration 1, 0.09 ml with the configuration 2, 0.03 mT with theconfiguration 3, 0.12 mT with the configuration 4, 0.27 ml with theconfiguration 5, 0.12 ml with the configuration 6, 0.42 mT with theconfiguration 7, and 0.34 mT with the configuration 8. It is understoodthat the leakage magnetic field intensity can be arbitrarily adjusted ina range from 4% to 60% of that for the ion gun to which the magneticshield is not added by selecting a structure of the magnetic shieldadded to the ion gun.

As described so far, according to the present embodiment, it is possibleto provide the ion milling system that includes the Penning dischargetype ion gun and that can reduce the leakage magnetic field from the iongun and sufficiently suppress the orbital shift of the electron beamemitted from the electron microscope column.

FIG. 11 shows an axial magnetic field intensity within the ion gun, inwhich (a) shows intensities in the cases of the configurations 3, 4, 5,and 8 and the case of the ion gun without the magnetic shield, and (b)shows intensities in the cases of the configurations 1, 2, 6, and 7 andthe case of the ion gun without the magnetic shield. The intensities areobtained as a result of calculating axial magnetic field intensities bythe magnetic field simulator in the case of employing the neodymiummagnet having the coercive force of 859 kA/m at the residual magneticflux density in the range from 1250 to 1320 mT as the permanent magnet114 mounted in the ion gun. In Z-axis coordinates indicated by ahorizontal axis of FIG. 11, a position at which the magnet is disposedis in a range from Z=−22.5 mm to −10.5 mm. This region functions as aplasma generation chamber within the ion gun. The axial magnetic fieldintensity is about 220 mT for the ion gun 101 to which the magneticshield is not added. On the other hand, the axial magnetic fieldintensity is about 120 mT for the magnetic shield structure ion gun withthe configuration 1, about 90 mT with configuration 2, about 60 mT withthe configuration 3, about 105 mT with the configuration 4, about 100 mTwith the configuration 5, about 180 mT with the configuration 6, about130 mT with the configuration 7, and about 140 mT with the configuration8. It is understood that the axial magnetic field intensity within themagnetic shield structure ion gun 100 can be arbitrarily adjusted in arange from 27% to 82% of that for the ion gun to which the magneticshield is not added by selecting the structure of the magnetic shieldadded to the ion gun.

A result of conducting a study about a relationship between the axialmagnetic field intensity and performances of the permanent magnet 114will next be explained. Table 1 shows a list of performance figures ofmagnets used. FIG. 12 shows a result of calculating the magnetic fieldintensities (magnetic flux densities) on a central axis of the ion gunby the magnetic field simulator in cases of incorporating, as thepermanent magnet 114, four types of magnets that are magnets A to Dshown in Table 1 into the ion gun 101 to which the magnetic shield isnot added. Numerical values shown in Table 1 are used as residualmagnetic flux densities and coercive forces used in calculation. In theZ-axis coordinates indicated by a horizontal axis of FIG. 12, theposition at which each magnet is disposed is in the range from Z=−22.5mm to −10.5 mm. This region functions as the plasma generation chamberwithin the ion gun, and the axial magnetic field intensity is about 220mT for the magnet A, about 195 mT for the magnet B, about 160 mT for themagnet C, and about 145 mT for the magnet D.

TABLE 1 magnet magnet A magnet B C magnet D maximum energy product:302-334 223-247 175-191 127-143 (BH)max (kJ/m3) residual magnetic1250-1320 1080-1150 ≥950 ≥850 flux density: Br (mT) coercive force: HcB(kA/m) ≥859 ≥796 ≥637 ≥660 axial magnetic flux 220 200 160 145 density(mT)

On the other hand, FIG. 13 shows a result of calculating the magneticfield intensities (magnetic flux densities) on the central axis of theion gun by the magnetic field simulator in cases of incorporating, asthe permanent magnet 114, the four types of magnets that are the magnetsA to D shown in Table 1 into the magnetic shield structure ion gun 100shown in the configuration 2 as an example of the present embodiment.The numerical values shown in Table 1 are used as the residual magneticflux densities and the coercive forces used in calculation. In Z-axiscoordinates indicated by a horizontal axis of FIG. 13, the position atwhich the magnet is disposed is in the range from Z=−22.5 mm to −10.5mm. This region functions as the plasma generation chamber within theion gun, and the axial magnetic field intensity is about 90 mT for themagnet A, about 80 mT for the magnet B, about 65 mT for the magnet C,and about 60 mT for the magnet D. It is understood that the axialmagnetic field intensity within the magnetic shield structure ion gun100 is reduced by about 41% from that within the ion gun to which themagnetic shield is not added by employing the magnetic shield structureion gun having the configuration 2, irrespectively of the type of themagnet. It is understood that the axial magnetic field intensity withinthe ion gun can be thereby arbitrarily adjusted in a wide range byselecting the type of the magnet and selecting the magnetic shieldstructure. Confining a combination between selection of the appropriatemagnetic field intensity and the appropriate ionization chamber inrelation to the selected ion gun configuration makes it possible toideally increase an amount of ions emitted from the ion gun. That is, inthis case, the magnetic shield configures a magnetic field control boardthat controls an axial magnetic field. It is thereby possible to controla processing rate in response to various use applications different in amaterial, a quality of the material, and the like of the sample to beprocessed. It is noted that this effect itself can be obtained withoutthe electron microscope.

FIG. 14 shows an example of a beam profile for explaining effects of thepresent embodiment, and shows a spot depth in an ion gun configurationsuch that the magnet B of Table 1 is mounted in the magnetic shieldstructure ion gun 100 shown in the configuration 2 as an example of thepresent embodiment. A conventional example shown in FIG. 14 indicates anion gun that is the ion gun 101 to which the magnetic shield is notadded and into which the magnet B of Table 1 is incorporated as thepermanent magnet 114. The ion gun configurations for both the presentembodiment and the conventional example were such that that an anodeinside diameter was 4 mm and a diameter of the anode outlet hole 131 was4 mm. The accelerating voltage was 6 kV, the discharge voltage was 1.5kV, and Ar gas at a flow rate of 0.07 cm³/minute was used as the gasintroduced into the ion gun. Silicon was used as a material to beprocessed, and milling processing was conducted without a mask that actsas a masking shield for 1 hour. In this way, the beam profiles wereobtained. A result shown in FIG. 14 indicates that a depth of a beamtrace is about 100 μm for the conventional example, while the depth ofthe beam trace is about 300 μm, that is, a recorded milling rate is 300μm/hour for the configuration 2, and that it is possible to obtain themilling rate about three times as high as that in the conventionalexample. Furthermore, a spot diameter of the ion beam is not reducedeven in this case.

As explained so far, according to the present embodiment, it is possibleto provide the ion milling system that can suppress the orbital shift ofthe electron beam emitted from the electron microscope column by addingthe magnetic shield structure to the ion gun. It is also possible tocontrol the axial magnetic field intensity within the ion gun to have anoptimum value by adding the magnetic shield structure to the ion gun.Furthermore, it is thereby possible to provide the Penning dischargetype ion milling system that can obtain the milling rate far higher thanthat according to the conventional technique or obtain the optimum valueof the milling rate in response to the various materials or the like.

Second Embodiment

An ion milling system according to a second embodiment of the presentinvention will be explained. It is noted that matters that are describedin the first embodiment but not described in the present embodiment arealso applicable to the present embodiment unless there are exceptionalcircumstances.

FIG. 15 is a cross-sectional configuration diagram showing an example ofan ion gun (including an accelerating electrode guide member) in the ionmilling system according to the present embodiment, and a configurationis basically similar to the configuration 2 shown in the firstembodiment. A difference between the configuration of the ion gun shownin FIG. 15 and the configuration 2 is that a magnetic shield typeaccelerating electrode 180 shown in FIG. 15 has a structure split intothree parts and has an accelerating electrode guide member 181, a firstaccelerating electrode member 182, and a second accelerating electrodemember 183.

The accelerating electrode guide member 181 is made of a material, forexample, stainless steel, other than the ferromagnetic substance andsecured to the ion gun base 117 by being screwed (or fitted) thereinto.The first accelerating electrode member 182 is formed from theferromagnetic substance, for example, pure iron, installed by beingfitted along an outer periphery of the accelerating electrode guidemember 181, and secured by the magnetic field of the permanent magnet114. The second accelerating electrode member 183 is formed from theferromagnetic substance, for example, pure iron, and has a structuresuch that the second accelerating electrode member 183 is positionedwith respect to the magnetic shield structure ion gun 100 by beingfitted into grooves formed in tip end portions of the acceleratingelectrode guide member 181 and the first accelerating electrode member182. Configuring the shield type accelerating electrode to have thestructure split into the three parts can facilitate attaching theaccelerating electrode guide member 181 formed from the material otherthan the ferromagnetic substance first without influence of thepermanent magnet 114 and attaching the first and second acceleratingelectrode members that are the magnetic material next using thisaccelerating electrode guide member. In other words, the magnetic shieldtype accelerating electrode 180 that is the ferromagnetic material canbe detached without interference of the permanent magnet 114 andmaintainability can be ensured.

FIG. 16 is a cross-sectional configuration diagram showing an example ofan ion gun (including the accelerating electrode guide member) in theion milling system according to the present embodiment, and aconfiguration is basically similar to the configuration 2 shown in thefirst embodiment. A difference between the configuration of the ion gunshown in FIG. 16 and the configuration 2 is that the magnetic shieldtype accelerating electrode 180 shown in FIG. 16 has a structure splitinto two parts and has the accelerating electrode guide member 181 andthe accelerating electrode member 182.

The accelerating electrode guide member 181 is made of a material, forexample, stainless steel other than the ferromagnetic substance andsecured to the ion gun base 117 by being screwed thereinto. Theaccelerating electrode member 182 is formed from the ferromagneticsubstance, for example, pure iron, and has a structure such that theaccelerating electrode member 182 is installed by being fitted into theion gun base 117 along the outer periphery of the accelerating electrodeguide member 181 and is positioned with respect to the magnetic shieldstructure ion gun 100 by being secured to the ion gun base 117 by themagnetic field of the permanent magnet 114. Configuring the shield typeaccelerating electrode 180 to have the structure split into the twoparts can facilitate attaching the accelerating electrode guide member181 formed from the material other than the ferromagnetic substancefirst without influence of the permanent magnet 114 and attaching theaccelerating electrode member 182 that is the magnetic material nextusing this accelerating electrode guide member 181. In other words, themagnetic shield type accelerating electrode 180 that is theferromagnetic material can be detached without the interference of thepermanent magnet 114 and the maintainability can be ensured. While theaccelerating electrode guide member is provided because of use of theaccelerating electrode as the magnetic shield in the present embodiment,similar effects can be basically obtained by providing a magnetic shieldguide member formed from a material other than the ferromagneticsubstance.

As explained so far, the present embodiment can exhibit similar effectsto those of the first embodiment. Furthermore, providing the magneticshield guide member such as the accelerating electrode guide memberformed from the material other than the ferromagnetic substance makes itpossible to facilitate attaching or detaching the ferromagnetic magneticshield and ensure maintainability.

The present invention is not limited to the embodiments described abovebut encompasses various modifications. For example, the abovementionedembodiments have been explained in detail for explaining the presentinvention so that the present invention is easy to understand. Thepresent invention is not always limited to the examples having all theconfigurations described so far. Furthermore, the configuration of thecertain embodiment can be partially replaced by the configuration of theother embodiment or the configuration of the other embodiment can beadded to the configuration of the certain embodiment. Moreover, for partof the configuration of each embodiment, additions, omissions, andsubstitutions of the other configurations can be made.

While the present invention has been explained in detail, the presentinvention includes the following aspects.

(1) An ion milling system including: an ion gun that includes apermanent magnet and that generates ions for processing a sample; and ascanning electron microscope that observes the sample, in which

the ion milling system includes a magnetic shield that reduces a leakagemagnetic field from the permanent magnet, and

the magnetic shield configures a magnetic field control board thatcontrols an axial magnetic field within the ion gun by changing astructure of the magnetic shield.

(2) An ion milling system including an ion gun that includes a permanentmagnet and that generates ions for processing a sample, in which

a magnetic field control board is disposed in such a manner thatmagnetic field control board surrounds an outer periphery of thepermanent magnet, is formed from a ferromagnetic material, and controlsan axial magnetic field intensity of the ion gun.

(3) The ion milling system according to (2), in which

the ion gun includes an accelerating electrode that accelerates theions; and an ion gun base that holds the permanent magnet and theaccelerating electrode, and

the magnetic field control board is also disposed on a surface, on aside of which the accelerating electrode is disposed, of the ion gunbase.

(4) The ion milling system according to (2), in which

the axial magnetic field intensity within the ion gun is controlled bychanging a structure of the magnetic field control board.

DESCRIPTION OF REFERENCE CHARACTERS

-   100: Magnetic shield structure ion gun-   101: Ion gun-   102: Ion beam-   103: Ion gun control section-   104: Vacuum chamber-   105: Evacuation system-   106: Sample-   107: Sample stage-   108: Sample stage drive section-   109: Sample stage drive control section-   111: First cathode-   112: Second cathode-   113: Anode-   114: Permanent magnet-   115: Accelerating electrode-   116: Insulator-   117: Ion gun base-   118: Ionization chamber-   119: Cathode ring-   121: Discharge power source-   122: Accelerating power source-   131: Anode outlet hole-   132: Cathode outlet hole-   133: Accelerating electrode outlet hole-   141: Gas supply mechanism-   142: Gas source-   151: Current measurement means-   152: Current probe drive section-   153: Current probe-   161: Electron microscope column-   162: Electron beam-   171, 172, 173, 174, 175, 176, 177: Magnetic shield-   181: Magnetic shield type accelerating electrode-   181: Accelerating electrode guide member-   182, 183: Accelerating electrode member

The invention claimed is:
 1. An ion milling system comprising: an ion gun that includes a permanent magnet and that generates ions for processing a sample; and a scanning electron microscope that observes the sample, wherein the ion milling system includes a magnetic shield that reduces a leakage magnetic field from the permanent magnet, the ion gun includes an accelerating electrode that accelerates the ions, and the magnetic shield is the accelerating electrode configured with a ferromagnetic material.
 2. The ion milling system according to claim 1, wherein the ion gun includes an ion gun base that holds the permanent magnet and the accelerating electrode, and a ferromagnetic material is disposed on a surface, on a side of which the accelerating electrode is disposed, of the ion gun base.
 3. The ion milling system according to claim 1, wherein the ion gun includes an ion gun base that holds the permanent magnet and the accelerating electrode, and the magnetic shield is configured with the ferromagnetic material with which an outer peripheral surface of the accelerating electrode and a surface, on a side of which the accelerating electrode is disposed, of the ion gun base are covered.
 4. The ion milling system according to claim 1, wherein the ion gun includes an ion gun base that holds the permanent magnet and the accelerating electrode, and the magnetic shield is configured with the ferromagnetic material with which an inner peripheral surface of the accelerating electrode and a surface, on a side of which the accelerating electrode is disposed, of the ion gun base are covered.
 5. The ion milling system according to claim 1, wherein the magnetic shield is configured with permalloy, pure iron, nickel, copper, molybdenum, and a material that contains at least one type of permalloy, pure iron, nickel, copper, and molybdenum as a main component.
 6. The ion milling system according to claim 1, wherein the ion gun includes an ion gun base that holds the permanent magnet and the accelerating electrode, the accelerating electrode is a structure split into three parts that are an accelerating electrode guide member, a first accelerating electrode member, and a second accelerating electrode member, the accelerating electrode guide member is formed from a material other than a ferromagnetic substance and secured to the ion gun base, the first accelerating electrode member is formed from the ferromagnetic substance and installed on an outer side of the accelerating electrode guide member, the second accelerating electrode member is formed from the ferromagnetic substance and installed by being positioned by the accelerating electrode guide member and the first accelerating electrode member, and the first and second accelerating electrode members are secured by a magnetic field of the permanent magnet.
 7. The ion milling system according to claim 1, wherein the magnetic shield includes a magnetic shield guide member that is disposed to surround an outer side of the permanent magnet and that is formed from a material other than a ferromagnetic material; and a magnetic shield member that is disposed to surround an outer side of the magnetic shield guide member and that is formed from the ferromagnetic material.
 8. An ion milling system comprising: an ion gun that includes a permanent magnet and that generates ions for processing a sample; and a scanning electron microscope that observes the sample, wherein the ion milling system includes a magnetic shield that reduces a leakage magnetic field from the permanent magnet, the ion gun includes an accelerating electrode that accelerates the ions; and an ion gun base that holds the permanent magnet and the accelerating electrode, and the magnetic shield is configured with a ferromagnetic material disposed on a surface, on a side of which the accelerating electrode is disposed, of the ion gun base, and a ferromagnetic material with which the accelerating electrode is covered and which is disposed apart from the accelerating electrode.
 9. An ion milling system comprising: an ion gun that includes a permanent magnet and that generates ions for processing a sample; and a scanning electron microscope that observes the sample, wherein the ion milling system includes a magnetic shield that reduces a leakage magnetic field from the permanent magnet, the ion gun includes a cathode ring that is disposed on an outer peripheral surface of the permanent magnet, and the magnetic shield is the cathode ring configured with a ferromagnetic material.
 10. An ion milling system comprising: an ion gun that includes a permanent magnet and that generates ions for processing a sample; and a scanning electron microscope that observes the sample, wherein the ion milling system includes a magnetic shield that reduces a leakage magnetic field from the permanent magnet, the magnetic shield is configured with a ferromagnetic material that surrounds an outer periphery of the permanent magnet and that is disposed apart from the permanent magnet, and the magnetic shield is on an inner side of an accelerating electrode.
 11. An ion milling system comprising: an ion gun that includes a permanent magnet and that generates ions for processing a sample; and a scanning electron microscope that observes the sample, wherein the ion milling system includes a magnetic shield that reduces a leakage magnetic field from the permanent magnet, and the magnetic shield configures a magnetic field control board that controls an axial magnetic field within the ion gun by changing a structure of the magnetic shield.
 12. An ion milling system comprising an ion gun that includes a permanent magnet and that generates ions for processing a sample, wherein a magnetic field control board is disposed in such a manner that magnetic field control board surrounds an outer periphery of the permanent magnet, is formed from a ferromagnetic material, and controls an axial magnetic field intensity within the ion gun.
 13. The ion milling system according to claim 12, wherein the ion gun includes an accelerating electrode that accelerates the ions; and an ion gun base that holds the permanent magnet and the accelerating electrode, and the magnetic field control board is also disposed on a surface, on a side of which the accelerating electrode is disposed, of the ion gun base.
 14. The ion milling system according to claim 12, wherein the axial magnetic field intensity within the ion gun is controlled by changing a structure of the magnetic field control board. 